American Journal of Botany 92(3): 558562. 2005.
NECTAR SPUR EVOLUTION IN THE MEXICAN LOBELIAS
MARGARET M. KOOPMAN2
AND TINA J. AYERS3
Department of Biological Sciences, P.O. Box 5640, Northern Arizona University, Flagstaff, Arizona 86011-5640 USA
Phylogenetic studies are often hampered by the independent evolution of characters that may potentially obscure relationships. The
adaptive significance of the nectar spur and its evolution within the Mexican lobeliads (Campanulaceae) is considered here. The
taxonomic delimitations of Heterotoma from the Mexican species within the genera Lobelia and Calcaratolobelia were tested. Inde-
pendent molecular data were gathered to determine whether the Mexican spurred lobeliads should be treated as distinct genera. The
internal transcribed spacer (ITS) region from 1826S nuclear rDNA and chloroplast DNA from the 3 trnK intron were sequenced
from 14 representative species. Our data suggest that Heterotoma, as originally conceived, is a good evolutionary unit within Lobelia
and that the presence of a nectar spur is an important morphological character that can be used in defining phylogenetic position. This
study also suggests that morphological changes associated with hummingbird pollination have evolved more than once in the Mexican
lobeliads, from small blue-flowered, insect-pollinated relatives.
Key words: Heterotoma; ITS; Lobelia; nectar spur; pollination; systematics; 3 trnK intron.
A fundamental objective in evolutionary biology is the ex-
amination and discovery of the causes and effects of species
origin. The use of phylogenetic data to study the evolution of